Various electric systems include switches that control conduction of electric currents to one or more loads. For example, in oil or gas mining operations, submersible pumps may be disposed in a well to remove oil or gas from the well. These pumps may be powered by three-phase electric currents supplied from power cables. The cables extend from power sources disposed outside of the well. The cables extend into the well to respective pumps in order to conduct the currents from the power sources to the machines. Typically, each three-phase cable powers a separate machine. As a result, each machine can be individually controlled by controlling when the current is conducted along the respective cable to the machine.
Because the pumps are located far from the power sources, the cables that supply the current to the pumps are very long. As the length of the cables increase, the cost to provide power to the pumps increases. In some systems, the cost of providing the cables of sufficient length to reach the pumps can be 40% or more of the total system cost, the system being comprised of the power source, cable, and motor-driven pump.
Additionally, the environment in which the pumps are located within the well can be harsh. The pumps can be exposed to temperatures in excess of 180 degrees Celsius, to pressure differentials on the order of 5,000 pounds per square inch, to mechanical vibrations, and the like. As a result, equipment that is placed into the well with the pumps needs to be able to operate in these extreme environments. Because of the harshness of this environment and the need for system reliability, if a first pump fails, it is advantageous to have a second pump installed. This is to avoid the costly and time consuming operation of retrieving the failed pump and replacing it. It is desirable to have a system where two redundant pumps may be installed with only a single power cable.